Effects of California thistle (Cirsium arvense) endophytes and environment on establishment of rust fungus, Puccinia punctiformis, a potential biocontrol agent

Abstract

Two genotypes of the noxious weed, Californian thistle (Cirsium arvense L. (Scop.)), were grown in either in a controlled environment glasshouse, as potted plants, or in soil, under natural, field conditions. All plants used in the trial had an existing natural titre of endophytes prior to artificial infection with the rust fungus, Puccinia punctiformis (F. Strauss) Röhl., a potential biocontrol agent for this invasive weed. Establishment of P. punctiformis was compared between genotypes (G27 and F1) and growing conditions (glasshouse and field). The number of endophytic genera were determined prior to trial commencement and completion, by morphological and molecular analyses. Inoculated G27 and F1 genotypes were visibly infected with P. punctiformis uredinia in glasshouse conditions after 11 days. Comparatively, P. punctiformis uredinia were only visible after 16 days under natural, field conditions. The rate of disease expression varied between the two genotypes, independent of growing conditions. Four weeks post-inoculation, G27 genotype showed more severe infection under natural field conditions than the F1 genotype (30% vs 9%, respectively; P=0.001) whereas F1 genotype showed greater infection severity than G27 under glasshouse conditions (37% vs 12%, respectively; P<0.001). G27 genotype had higher levels of disease expression infection in the field compared to plants of the same genotype in the glasshouse (30% vs 12%, respectively; P<0.001). Data analysis determined distinct differences in the number of recovered endophytes, dependent on the environment and genotype.